The present invention relates to a magnetic head unit having a magnetic impedance element and for reproducing information recorded on a magnetic recording medium, a method of manufacturing the same and a magnetic recording and reproducing apparatus using the same.
As a magnetic head for a magnetic recording and reproducing apparatus such as a hard disk drive, an inductive magnetic head has been used such as a ferrite head, a MIG (metal-in-gap) head and a thin-film head. These inductive magnetic heads, however, have a problem that when a relative speed is reduced with respect to a magnetic recording medium, an output of a reproduction signal is reduced, so that a reproducing sensitivity degrades.
In order to improve the problem, a conventional integrated magnetic head has been developed and put to practical use. The conventional integrated magnetic head comprises an inductive magnetic head and a magneto-resistive head (hereinafter referred to as "MR head") using a magneto-resistive element. In the conventional integrated magnetic head as disclosed, for example, in a technical report of the magnetics society of Japan, 1991, Vol. 15, No. 2, pp. 141-144, the MR head reproduces information from the magnetic recording medium such as a magnetic tape and the inductive magnetic head records information onto the magnetic recording medium.
A conventional magnetic head unit using the above-mentioned integrated magnetic head will be explained with reference to FIG. 12A, FIG. 12B, FIG. 13A and FIG. 13B concretely.
FIG. 12A is a perspective view showing a configuration of a conventional magnetic head unit. FIG. 12B is a cross-sectional view showing a cross section of a conventional head suspension, taken on the dash and dotted line XIIB of FIG. 12A. FIG. 13A is a cross-sectional view showing a configuration of a principal part of a conventional integrated magnetic head. FIG. 13B is an enlarged perspective view schematically showing a configuration of a MR head shown in FIG. 13A.
In FIG. 12A and FIG. 12B, the conventional magnetic head unit 70 comprises a head slider 72 having an integrated magnetic head 71 mounted thereon, and a head suspension 73 for suspending the head slider 72. The integrated magnetic head 71 is connected to an electric circuit (not shown) such as a reproducing circuit by a metal strand 74. The head slider 72 is attached to an end part of the head suspension 73 by a non-illustrated known head gimbal so that the integrated magnetic head 71 is positioned at a tip end portion of the head suspension 73. The head suspension 73 is made of a metal such as stainless steel and has a screw hole 73a for attaching the head suspension 73 to a rotary arm (not shown) at the other end part thereof. The head suspension 73 also has folded parts 73b for disposing the metal strand 74.
As shown in FIG. 13A and FIG. 13B, the conventional integrated magnetic head 71 comprises an inductive magnetic head 75 for recording information and a MR head 76 for reproducing information. The integrated magnetic head 71 is disposed over a magnetic recording medium 77 such as a magnetic tape so that below-mentioned first and second magnetic gaps 81 and 83 are faced to a magnetic layer 77b provided on a substrate 77a of the magnetic recording medium 77.
The inductive magnetic head 75 comprises first and second magnetic yokes 78 and 79, a winding 80 wound around the first magnetic yoke 78, and the first recording magnetic gap 81 for provided between the first magnetic yoke 78 and the second magnetic yoke 79.
The MR head 76 comprises a ferrite substrate 82, the second reproduction magnetic gap 83 for provided between the second magnetic yoke 79 and the ferrite substrate 82, and a MR element 84 provided in the second magnetic gap 83. The MR element 84 comprises a MR film 84a, a pair of hard magnetic films 84b provided at the end parts of the MR film 84a, and a pair of conductor thin films 84c connected to the end parts of the MR film 84a. The MR film 84a is configured with a high permeability material e.g. by a permalloy film and the like. The electrical resistance of the MR film 84a varies in accordance with the magnetic flux of a signal magnetization 85 formed in the magnetic layer 77b facing to the MR film 84a. In reproducing information, a predetermined current is passed through the MR film 84a from the conductor thin film 84c. The hard magnetic film 84b changes and maintains magnetic domain in the MR film 84a to a single magnetic domain.
An operation of the conventional integrated magnetic head 71 will be explained.
In recording information onto the magnetic recording medium 77, a signal current corresponding to the information is supplied to the winding 80, so that a signal magnetic field is generated and leaked from the first magnetic gap 81. Consequently, the signal magnetization 85 is formed in the magnetic layer 77b of the magnetic recording medium 77 facing to the first magnetic gap 81, so that the information is recorded onto the magnetic recording medium 77.
In reproducing information from the magnetic recording medium 77, the electrical resistance of the MR film 84a varies in accordance with the magnetic flux generated from the signal magnetization 85 flowing from the second magnetic gap 83. Thereby, the current passing through the conductor thin film 84c varies. By detecting a variation in the current with a non-illustrated detecting circuit, a reproduction signal corresponding to the information is produced and the reproduction signal is output.
Thus, in the conventional integrated magnetic head 71 using the MR head 76, since the magnetic flux flowing into the MR film 84a is electromagnetically converted and output as the reproduction signal, a high-output reproduction signal is obtained irrespective of the relative speed with respect to the magnetic recording medium 77. For this reason, the information is reproduced with the reproducing sensitivity approximately three to ten times that of the previously-described inductive magnetic head. In recent years, a giant MR element has been being developed which element is capable of improving the reproducing sensitivity three to ten times that of the MR head 76.
However, the conventional integrated magnetic head 71 having the MR head 76 has a problem that a head structure is complicated compared with the conventional inductive magnetic head. Specifically, in the conventional integrated magnetic head 71, it is necessary to provide the second magnetic gap 83 for reproduction and a non-illustrated shield layer around the MR element 84 and it is also necessary to provide the hard magnetic film 84b in order that the magnetic domain of the MR film 84a is a single magnetic domain. Further, in order to perform reproduction with a linear characteristic, it is necessary to provide a bias layer (not shown) for applying a bias magnetic field and a power source (not shown) for supplying direct current to the bias layer.
In addition, according to a method for manufacturing the conventional integrated magnetic head 71, in order to obtain an excellent magnetic characteristic (reproducing sensitivity), it is necessary to heat the second magnetic yoke 79 and the ferrite substrate 82 provided around the MR element 84.
As a conventional reproducing head intended to solve the problem, such a magnetic impedance head (hereinafter referred to as "MI head") is known that which uses a magnetic impedance element for detecting a variation in magnetic impedance. The conventional MI head was proposed, for example, in a technical report of Institute of Electronics Information and Communication Engineers, Japan, MR95-85.
The conventional MI head will be elucidated with reference to FIG. 14A and FIG. 14B.
FIG. 14A is an explanatory view schematically showing a configuration of a conventional reproducing head using a magnetic impedance element. FIG. 14B is an enlarged view showing a configuration of a soft magnetic core encircled by a dashed line XIVB of FIG. 14A.
In FIG. 14A and FIG. 14B, a conventional MI head 86 comprises a conductor thin film 86a which is a thin film of an electrically conductive metal such as copper, and first and second soft magnetic cores 86b and 86c magnetically coupled to each other and sandwiching the conductor thin film 86a therebetween. One end of the conductor thin film 86a is connected to an end of a high-frequency signal generator 87, and the other end is connected to the other end of the high-frequency signal generator 87 through a resistor 88. The high-frequency signal generator 87 generates a UHF-band high-frequency signal (carrier signal) which is a constant or steady state AC current, and supplies the signal to the conductor thin film 86a. To the one and the other ends of the conductor thin film 86a, terminals 90a and 90b for detecting the variation in the magnetic impedance are connected by lead wires 89a and 89b, respectively. The variation in the magnetic impedance is detected by detecting a variation in voltage between the terminals 90a and 90b. The terminals 90a and 90b are connected to a reproduction signal detecting circuit (not shown) and the reproduction signal is produced based on the variation in the voltage. On the high-frequency signal from the high-frequency signal generator 87, for example, a minute bias DC current is superimposed for biasing the respective magnetizations of the first and second soft magnetic cores 86b and 86c in a predetermined direction. Consequently, the voltage detected between the terminal 90a and 90b varies in accordance with the polarity of the signal magnetization 85 recorded on the magnetic recording medium 77.
The first and second soft magnetic cores 86b and 86c are magnetic cores made of a magnetic material having a high magnetic susceptibility. Specifically, the first and second soft magnetic cores 86b and 86c are laminated films having permalloy films 86d and SiO2 films 86e formed alternately. Dimensions (represented by "P" in FIG. 14A) of the surfaces of the first and second soft magnetic cores 86b and 86 faced to the magnetic recording medium 77 are set so as to equal the width of a track 77c of the magnetic recording medium 77. The easy axes of magnetization in the first and second soft magnetic cores 86b and 86c align parallel to the width of the track 77c. The first and second soft magnetic cores 86b and 86c are electrically insulated from the conductor thin film 86a by a non-illustrated insulating film.
Subsequently, a reproducing operation of the MI head 86 will be described.
When the MI head 86 scans the magnetic recording medium 77, the magnetic flux of the signal magnetization 85 of the magnetic recording medium 77 is passed through the first and second soft magnetic cores 86b and 86c. Consequently, the respective magnetizations in the first and second soft magnetic cores 86b and 86c are inclined from the direction of alignment by the magnetic flux of the signal magnetization 85, so that the impedance of the MI head 86 decreases.
At this time, since the conductor thin film 86a is supplied with the constant AC current from the high-frequency signal generator 87, a drop of voltage proportional to the impedance of the MI head 86 is generated between the terminals 90a and 90b. Accordingly, when the MI head 86 relatively scans the signal magnetization 85 having different polarity and magnitude, the variation in the voltage between the terminals 90a and 90b forms an amplitude modulation wave (hereinafter referred to as "AM wave") with the high-frequency signal current from the high-frequency signal generator 87 as the carrier. The AM wave is demodulated as the reproduction signal at the reproduction signal detecting circuit. When no information is recorded on the magnetic recording medium 77 and the magnetic flux of the signal magnetization 85 is not present, a voltage corresponding to the product of the constant current of the high-frequency signal from the high-frequency signal generator 87 and the impedance between the terminals 90a and 90b is generated between the terminals 90a and 90b.
Thus, the MI head 86 is a reproducing head of a magnetic flux response type directly using the magnetic flux of the signal magnetization 85 without any magnetic gap for reproduction and shielding layer. Moreover, in the portion of the MI head 86 succeeding the terminals 90a and 90b for detection, as described above, the reproduction signal is produced by demodulating the AM wave. For this reason, in the MI head 86, the output of the reproduction signal is easily increased. For example, it is expected that an output is obtained which is approximately ten times that of the reproducing head using the giant MR element.
However, in the MI head 86, since the high-frequency signal generated by the high-frequency signal generator 87 is used, there occurs problems that electromagnetic radiation is caused by the high-frequency signal and external noises readily intrude. Further, when the MI head 86 is mounted on the conventional head suspension 73 shown in FIG. 12A, the head suspension 73 functions as an antenna, so that a sufficient signal-to-noise ratio cannot be obtained due to the electromagnetic radiation and the external noises. In addition, a transmission line for transmitting the high-frequency signal (current signal) supplied to the MI head 86 and a transmission line for transmitting the high-frequency signal (voltage signal) output from the MI head 86 form a distributed element circuit and perform impedance matching so that no loss is produced due to a reflected wave on the transmission lines.
The electromagnetic radiation can be suppressed by using a coaxial cable as the transmission lines. However, since the existing coaxial cables are great in diameter, it is difficult to mount the existing coaxial cables on the conventional head suspension 73. Further, the coaxial cable is high in stiffness and heavy in weight compared with the metal strand 74 shown in FIG. 12A. For this reason, the coaxial cable can hinder the head suspension from performing the seek operation at high speed. In addition, the coaxial cable, which increases the load imposed on the head suspension because of it weight, can make it difficult to adjust the distance between the magnetic head and the surface of the magnetic recording medium, namely, flying height of the magnetic head during operation. When the coaxial cable is reduced in diameter so that it can be mounted on the head suspension 73, the loss of the transmitted signal increases and the cost increases.